extremely gradual process of erosion the surface waters have been for ages constantly dissolving and removing this rock, and depositing in its place the iron which they derived from the upper portions of the iron-bearing stratum. It is simply another example of the process of replacement or substitution already described, and which, as we shall see, has played an important part in forming and enriching many of the metalliferous and other valuable deposits worked by man. The famous Mesabi Range of Minnesota, and mines in other districts in the Lake Superior region, furnish examples where this can be proved to have taken place on a huge scale.

Sometimes these masses of iron ore, especially when contained in the older rocks, are several hundred feet in thickness, and have great longitudinal extension. The ore usually varies from a pure magnetic oxide or magnetite, to what is known as a specular ore, or red hematite, or admixtures of these varieties. The latter (red hematite) is sometimes soft and sometimes hard, but more frequently hard. Often portions of these deposits, and especially deposits of the class to which reference will presently be made, are what is known as brown hematite, or limonite (from leimon, a meadow). Brown hematite ore is the chief ore of the southern United States, and in some cases seems to be due to the oxidation of an original carbonate ore. In the great majority of cases in the southern United States this ore, as well as the socalled "fossiliferous" ore (impure red hematite), is found in rather irregular stratified deposits; but doubtless many of these deposits, like other iron deposits, have been enriched in the way above referred to.

(b.) Deposits of the second class are those where the iron ore is simply and certainly due to the oxidation of original iron pyrites, to which mineral reference has already been made under the head. of sulphur. This iron pyrites, when subjected to the oxidizing influence of the atmosphere and of surface waters, loses its sulphur and becomes oxide of iron, that is, ordinary iron ore. This may be a hydrated oxide, or by heat and by pressure, or other causes, the water may have been driven off, leaving it in the form of either magnetic or specular iron ore. A very considerable number of the iron deposits of the world are of this character, but in many, oxidation has proceeded to such a depth that mining 1 It also frequently represents the oxidation of iron pyrites.

has not yet developed the absolutely unaltered iron pyrites, although this mineral often increases in abundance as depth is attained. For example, there is a huge cap of iron ore on the famous deposit of iron pyrites at Rio Tinto, Spain. Examples of this kind are more or less common throughout the Rocky Mountain region. Undoubtedly many deposits of brown hematite, red hematite, and of magnetic iron ore, some of great magnitude, are of this class.1

Iron ore in its legal aspect is interesting, especially in the western United States; for in the eastern portion of the country, as will be seen hereafter, it matters little what the kind of deposit may be, owing to the fact that the common law rules that a man owns where there has been no severance of the mineral estate from the ownership of the soil-all that may be found within his boundary lines extended vertically downward. It has, however, never been judicially decided whether an iron ore deposit valuable for no other metal which it may contain, should be located as a lode or placer deposit when upon government lands. Where it is certainly due to the oxidation of masses of original iron pyrites filling crevices or collected along some line of contact, as between an eruptive rock and limestone, and especially when it carries some other valuable metals, it would certainly seem that, if it is sufficiently continuous, it should be properly located as a lode claim, and not as a placer claim.

The following diagrams will illustrate very roughly the usual manner of occurrence of iron ore and make it more easy to understand the above distinctions.

1 These three ores when chemically metallic iron. It is very high grade ore pure that is, when the iron contained in them is united only with oxygen, which purity is never met with can respectively contain 59.8, 70, and 72.4 per cent of

of either class that shows a percentage six or seven units less than the possibilities mentioned.

Occurrence of more or less Stratified and Pockety or Irregular
Deposits.

Mode of Occurrence of Contact Iron Ore Deposits which are certainly due to the Oxidation of Iron Pyrites.

Manganese. The principal use of this quite important metal is in the manufacture of steel.

It is derived principally from two ores, oxide of manganese and carbonate of manganese. These ores, especially the former, occur quite abundantly in nature, although nothing like to the same extent as iron.

The chief supply of manganese is drawn from perfectly stratified sedimentary beds, as in Chile, Russia, Cuba, etc., although in the United States its occurrence is very much more pockety. In this country it is chiefly found in beds of clay resulting from the disintegration of some certain kind of rock, which may be either original sandstone, as in Virginia, or limestone, as in Arkansas. It is chiefly found in irregular masses varying from less than an ounce to many tons in weight. There is, however, every reason to believe that the manganese was in the original rock which has dissolved into clay; that is to say, when this rock rotted into clay the manganese ore remained in the latter in some cases in somewhat the same position as it was originally deposited in the sedimentary material which was afterward consolidated into hard.

rock. But it is much more probable, in the majority of cases, that what has been referred to as the process of superficial enrichment may have taken place in the majority of these deposits in somewhat the same manner as in the iron ore deposits which have already been described, so that these nodular masses of manganese ore in the clay represent the segregation of this material, the rock which originally contained it having contained it in a much more disseminated condition. These masses are therefore much larger and more abundant than they would have been otherwise.1

The ore is usually confined to a certain stratum or certain strata in a series of sedimentary rocks, and it adheres to these strata with great pertinacity. This is simply due to the fact that the conditions for the deposition or precipitation of manganese ore were present when these particular sediments were deposited, and were not present when either the older or younger sediments were deposited. Whether the ore was originally deposited in the form of a carbonate or as an oxide is not proven, though many think that, as in the case of some iron ores, it was originally deposited in the form of a carbonate and has been subsequently changed to an oxide. This, however, is of small importance here.

The other class of deposits are carbonate and silicate of manganese. The latter has never been used as a manganese ore, although it is quite common in our western United States, where it often marks the outcrops of fissure veins, having been oxidized superficially to the common black oxide of manganese. It is usually very impure. The deposits of carbonate of manganese are beginning to attract attention. For example, in the

1 The peculiar mammillated or rounded appearance of these nodules lends force to this theory.

Pyrenees they are being worked quite extensively at the present time.

The mining of manganese ore in this country has so far presented very few legal difficulties, for the simple reason that all the deposits of this mineral have been usually in the eastern portion of the United States, where, as has been stated, the commonlaw maxim of cujus est solum ejus est usque ad cœlum prevails. Upon lands belonging to the government there are, however, in the western United States, deposits of very impure manganese ore, which mark the outcroppings of some fissure vein (e. g. near Butte and elsewhere in Montana) or more irregular pockety deposits (e. g. in the Leadville district), as above stated. Should these classes of deposits ever possess value, the law applicable to lode claims would usually prevail, unless, as in the case of some iron or of the more valuable ores, the deposit should be of such a pockety or bunchy, that is to say irregular, discontinuous type, as to make this improper.1 This will be made clear hereafter in discussing vein and kindred deposits.

Attention is simply called to the fact that deposits of manganese ore, which are valuable for the manganese which they contain, like some beds of iron ore, are in the great majority of cases found forming distinctly stratified beds or parts of a distinctly stratified stratum, or in the clay derived from the decay of such a stratum; and hence when so found upon government lands it would appear that the law as to the location of a lode claim should not be applicable to them, for the same reason that it should not be applicable to stratified beds or pockety deposits of iron ore, as distinct from iron ore found as the capping of a fissure vein or true lode. When so found, therefore, manganese deposits should, generally speaking, be located as placer claims.

Aluminum. The ores from which this metal is extracted are rapidly assuming commercial importance. At present there are but two ores of aluminum broadly considered. One is known as cryolite, a large deposit of which is found in Greenland, but which is not common elsewhere. This mineral is composed of sodium, aluminum, and fluorine. As it is not found in large

1 The ore in the croppings of fissure veins is, however, so impure and superficial that it is not likely ever to possess

much value as manganese ore, though it is often valuable for the silver and other metals with which it is associated.